An animation that supports only forward steps. A forward animation implements
the methods hasNextStep and nextStep using the state
pattern with instances of interface Step being the states. A forward
animation starts at a first step and delegates calls to hasNextStep
and nextStep to a Step instance that changes upon every
call to nextStep.

ForwardAnimation

public ForwardAnimation()

Default constructor; does nothing. Note that as long as this animation's
first step is not properly initialized (i.e. assigned a non-null value)
every attempt to call hasNextStep or nextStep will
throw IllegalStateException. You can initalize this animation's
first step anytime this animation is in a cleared state, i.e. after
initialization or after a call to clear as long as
nextStep hasn't been called.

ForwardAnimation

Initializes this animation with the specified initial step. Note that as
long as this animation's first step is not properly initialized (i.e.
assigned a non-null value) every attempt to call hasNextStep or
nextStep will throw IllegalStateException. You can
initalize this animation's first step anytime this animation is in a
cleared state, i.e. after initialization or after a call to
clear as long as nextStep hasn't been called.